8187443: Forest Consolidation: Move files to unified layout
Reviewed-by: darcy, ihse
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent;
import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Consumer;
import java.util.function.Predicate;
/**
* An optionally-bounded {@linkplain BlockingDeque blocking deque} based on
* linked nodes.
*
* <p>The optional capacity bound constructor argument serves as a
* way to prevent excessive expansion. The capacity, if unspecified,
* is equal to {@link Integer#MAX_VALUE}. Linked nodes are
* dynamically created upon each insertion unless this would bring the
* deque above capacity.
*
* <p>Most operations run in constant time (ignoring time spent
* blocking). Exceptions include {@link #remove(Object) remove},
* {@link #removeFirstOccurrence removeFirstOccurrence}, {@link
* #removeLastOccurrence removeLastOccurrence}, {@link #contains
* contains}, {@link #iterator iterator.remove()}, and the bulk
* operations, all of which run in linear time.
*
* <p>This class and its iterator implement all of the <em>optional</em>
* methods of the {@link Collection} and {@link Iterator} interfaces.
*
* <p>This class is a member of the
* <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
* Java Collections Framework</a>.
*
* @since 1.6
* @author Doug Lea
* @param <E> the type of elements held in this deque
*/
public class LinkedBlockingDeque<E>
extends AbstractQueue<E>
implements BlockingDeque<E>, java.io.Serializable {
/*
* Implemented as a simple doubly-linked list protected by a
* single lock and using conditions to manage blocking.
*
* To implement weakly consistent iterators, it appears we need to
* keep all Nodes GC-reachable from a predecessor dequeued Node.
* That would cause two problems:
* - allow a rogue Iterator to cause unbounded memory retention
* - cause cross-generational linking of old Nodes to new Nodes if
* a Node was tenured while live, which generational GCs have a
* hard time dealing with, causing repeated major collections.
* However, only non-deleted Nodes need to be reachable from
* dequeued Nodes, and reachability does not necessarily have to
* be of the kind understood by the GC. We use the trick of
* linking a Node that has just been dequeued to itself. Such a
* self-link implicitly means to jump to "first" (for next links)
* or "last" (for prev links).
*/
/*
* We have "diamond" multiple interface/abstract class inheritance
* here, and that introduces ambiguities. Often we want the
* BlockingDeque javadoc combined with the AbstractQueue
* implementation, so a lot of method specs are duplicated here.
*/
private static final long serialVersionUID = -387911632671998426L;
/** Doubly-linked list node class */
static final class Node<E> {
/**
* The item, or null if this node has been removed.
*/
E item;
/**
* One of:
* - the real predecessor Node
* - this Node, meaning the predecessor is tail
* - null, meaning there is no predecessor
*/
Node<E> prev;
/**
* One of:
* - the real successor Node
* - this Node, meaning the successor is head
* - null, meaning there is no successor
*/
Node<E> next;
Node(E x) {
item = x;
}
}
/**
* Pointer to first node.
* Invariant: (first == null && last == null) ||
* (first.prev == null && first.item != null)
*/
transient Node<E> first;
/**
* Pointer to last node.
* Invariant: (first == null && last == null) ||
* (last.next == null && last.item != null)
*/
transient Node<E> last;
/** Number of items in the deque */
private transient int count;
/** Maximum number of items in the deque */
private final int capacity;
/** Main lock guarding all access */
final ReentrantLock lock = new ReentrantLock();
/** Condition for waiting takes */
private final Condition notEmpty = lock.newCondition();
/** Condition for waiting puts */
private final Condition notFull = lock.newCondition();
/**
* Creates a {@code LinkedBlockingDeque} with a capacity of
* {@link Integer#MAX_VALUE}.
*/
public LinkedBlockingDeque() {
this(Integer.MAX_VALUE);
}
/**
* Creates a {@code LinkedBlockingDeque} with the given (fixed) capacity.
*
* @param capacity the capacity of this deque
* @throws IllegalArgumentException if {@code capacity} is less than 1
*/
public LinkedBlockingDeque(int capacity) {
if (capacity <= 0) throw new IllegalArgumentException();
this.capacity = capacity;
}
/**
* Creates a {@code LinkedBlockingDeque} with a capacity of
* {@link Integer#MAX_VALUE}, initially containing the elements of
* the given collection, added in traversal order of the
* collection's iterator.
*
* @param c the collection of elements to initially contain
* @throws NullPointerException if the specified collection or any
* of its elements are null
*/
public LinkedBlockingDeque(Collection<? extends E> c) {
this(Integer.MAX_VALUE);
addAll(c);
}
// Basic linking and unlinking operations, called only while holding lock
/**
* Links node as first element, or returns false if full.
*/
private boolean linkFirst(Node<E> node) {
// assert lock.isHeldByCurrentThread();
if (count >= capacity)
return false;
Node<E> f = first;
node.next = f;
first = node;
if (last == null)
last = node;
else
f.prev = node;
++count;
notEmpty.signal();
return true;
}
/**
* Links node as last element, or returns false if full.
*/
private boolean linkLast(Node<E> node) {
// assert lock.isHeldByCurrentThread();
if (count >= capacity)
return false;
Node<E> l = last;
node.prev = l;
last = node;
if (first == null)
first = node;
else
l.next = node;
++count;
notEmpty.signal();
return true;
}
/**
* Removes and returns first element, or null if empty.
*/
private E unlinkFirst() {
// assert lock.isHeldByCurrentThread();
Node<E> f = first;
if (f == null)
return null;
Node<E> n = f.next;
E item = f.item;
f.item = null;
f.next = f; // help GC
first = n;
if (n == null)
last = null;
else
n.prev = null;
--count;
notFull.signal();
return item;
}
/**
* Removes and returns last element, or null if empty.
*/
private E unlinkLast() {
// assert lock.isHeldByCurrentThread();
Node<E> l = last;
if (l == null)
return null;
Node<E> p = l.prev;
E item = l.item;
l.item = null;
l.prev = l; // help GC
last = p;
if (p == null)
first = null;
else
p.next = null;
--count;
notFull.signal();
return item;
}
/**
* Unlinks x.
*/
void unlink(Node<E> x) {
// assert lock.isHeldByCurrentThread();
// assert x.item != null;
Node<E> p = x.prev;
Node<E> n = x.next;
if (p == null) {
unlinkFirst();
} else if (n == null) {
unlinkLast();
} else {
p.next = n;
n.prev = p;
x.item = null;
// Don't mess with x's links. They may still be in use by
// an iterator.
--count;
notFull.signal();
}
}
// BlockingDeque methods
/**
* @throws IllegalStateException if this deque is full
* @throws NullPointerException {@inheritDoc}
*/
public void addFirst(E e) {
if (!offerFirst(e))
throw new IllegalStateException("Deque full");
}
/**
* @throws IllegalStateException if this deque is full
* @throws NullPointerException {@inheritDoc}
*/
public void addLast(E e) {
if (!offerLast(e))
throw new IllegalStateException("Deque full");
}
/**
* @throws NullPointerException {@inheritDoc}
*/
public boolean offerFirst(E e) {
if (e == null) throw new NullPointerException();
Node<E> node = new Node<E>(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
return linkFirst(node);
} finally {
lock.unlock();
}
}
/**
* @throws NullPointerException {@inheritDoc}
*/
public boolean offerLast(E e) {
if (e == null) throw new NullPointerException();
Node<E> node = new Node<E>(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
return linkLast(node);
} finally {
lock.unlock();
}
}
/**
* @throws NullPointerException {@inheritDoc}
* @throws InterruptedException {@inheritDoc}
*/
public void putFirst(E e) throws InterruptedException {
if (e == null) throw new NullPointerException();
Node<E> node = new Node<E>(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
while (!linkFirst(node))
notFull.await();
} finally {
lock.unlock();
}
}
/**
* @throws NullPointerException {@inheritDoc}
* @throws InterruptedException {@inheritDoc}
*/
public void putLast(E e) throws InterruptedException {
if (e == null) throw new NullPointerException();
Node<E> node = new Node<E>(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
while (!linkLast(node))
notFull.await();
} finally {
lock.unlock();
}
}
/**
* @throws NullPointerException {@inheritDoc}
* @throws InterruptedException {@inheritDoc}
*/
public boolean offerFirst(E e, long timeout, TimeUnit unit)
throws InterruptedException {
if (e == null) throw new NullPointerException();
Node<E> node = new Node<E>(e);
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (!linkFirst(node)) {
if (nanos <= 0L)
return false;
nanos = notFull.awaitNanos(nanos);
}
return true;
} finally {
lock.unlock();
}
}
/**
* @throws NullPointerException {@inheritDoc}
* @throws InterruptedException {@inheritDoc}
*/
public boolean offerLast(E e, long timeout, TimeUnit unit)
throws InterruptedException {
if (e == null) throw new NullPointerException();
Node<E> node = new Node<E>(e);
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (!linkLast(node)) {
if (nanos <= 0L)
return false;
nanos = notFull.awaitNanos(nanos);
}
return true;
} finally {
lock.unlock();
}
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E removeFirst() {
E x = pollFirst();
if (x == null) throw new NoSuchElementException();
return x;
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E removeLast() {
E x = pollLast();
if (x == null) throw new NoSuchElementException();
return x;
}
public E pollFirst() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return unlinkFirst();
} finally {
lock.unlock();
}
}
public E pollLast() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return unlinkLast();
} finally {
lock.unlock();
}
}
public E takeFirst() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lock();
try {
E x;
while ( (x = unlinkFirst()) == null)
notEmpty.await();
return x;
} finally {
lock.unlock();
}
}
public E takeLast() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lock();
try {
E x;
while ( (x = unlinkLast()) == null)
notEmpty.await();
return x;
} finally {
lock.unlock();
}
}
public E pollFirst(long timeout, TimeUnit unit)
throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
E x;
while ( (x = unlinkFirst()) == null) {
if (nanos <= 0L)
return null;
nanos = notEmpty.awaitNanos(nanos);
}
return x;
} finally {
lock.unlock();
}
}
public E pollLast(long timeout, TimeUnit unit)
throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
E x;
while ( (x = unlinkLast()) == null) {
if (nanos <= 0L)
return null;
nanos = notEmpty.awaitNanos(nanos);
}
return x;
} finally {
lock.unlock();
}
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E getFirst() {
E x = peekFirst();
if (x == null) throw new NoSuchElementException();
return x;
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E getLast() {
E x = peekLast();
if (x == null) throw new NoSuchElementException();
return x;
}
public E peekFirst() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return (first == null) ? null : first.item;
} finally {
lock.unlock();
}
}
public E peekLast() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return (last == null) ? null : last.item;
} finally {
lock.unlock();
}
}
public boolean removeFirstOccurrence(Object o) {
if (o == null) return false;
final ReentrantLock lock = this.lock;
lock.lock();
try {
for (Node<E> p = first; p != null; p = p.next) {
if (o.equals(p.item)) {
unlink(p);
return true;
}
}
return false;
} finally {
lock.unlock();
}
}
public boolean removeLastOccurrence(Object o) {
if (o == null) return false;
final ReentrantLock lock = this.lock;
lock.lock();
try {
for (Node<E> p = last; p != null; p = p.prev) {
if (o.equals(p.item)) {
unlink(p);
return true;
}
}
return false;
} finally {
lock.unlock();
}
}
// BlockingQueue methods
/**
* Inserts the specified element at the end of this deque unless it would
* violate capacity restrictions. When using a capacity-restricted deque,
* it is generally preferable to use method {@link #offer(Object) offer}.
*
* <p>This method is equivalent to {@link #addLast}.
*
* @throws IllegalStateException if this deque is full
* @throws NullPointerException if the specified element is null
*/
public boolean add(E e) {
addLast(e);
return true;
}
/**
* @throws NullPointerException if the specified element is null
*/
public boolean offer(E e) {
return offerLast(e);
}
/**
* @throws NullPointerException {@inheritDoc}
* @throws InterruptedException {@inheritDoc}
*/
public void put(E e) throws InterruptedException {
putLast(e);
}
/**
* @throws NullPointerException {@inheritDoc}
* @throws InterruptedException {@inheritDoc}
*/
public boolean offer(E e, long timeout, TimeUnit unit)
throws InterruptedException {
return offerLast(e, timeout, unit);
}
/**
* Retrieves and removes the head of the queue represented by this deque.
* This method differs from {@link #poll() poll()} only in that it throws an
* exception if this deque is empty.
*
* <p>This method is equivalent to {@link #removeFirst() removeFirst}.
*
* @return the head of the queue represented by this deque
* @throws NoSuchElementException if this deque is empty
*/
public E remove() {
return removeFirst();
}
public E poll() {
return pollFirst();
}
public E take() throws InterruptedException {
return takeFirst();
}
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
return pollFirst(timeout, unit);
}
/**
* Retrieves, but does not remove, the head of the queue represented by
* this deque. This method differs from {@link #peek() peek()} only in that
* it throws an exception if this deque is empty.
*
* <p>This method is equivalent to {@link #getFirst() getFirst}.
*
* @return the head of the queue represented by this deque
* @throws NoSuchElementException if this deque is empty
*/
public E element() {
return getFirst();
}
public E peek() {
return peekFirst();
}
/**
* Returns the number of additional elements that this deque can ideally
* (in the absence of memory or resource constraints) accept without
* blocking. This is always equal to the initial capacity of this deque
* less the current {@code size} of this deque.
*
* <p>Note that you <em>cannot</em> always tell if an attempt to insert
* an element will succeed by inspecting {@code remainingCapacity}
* because it may be the case that another thread is about to
* insert or remove an element.
*/
public int remainingCapacity() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return capacity - count;
} finally {
lock.unlock();
}
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public int drainTo(Collection<? super E> c) {
return drainTo(c, Integer.MAX_VALUE);
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public int drainTo(Collection<? super E> c, int maxElements) {
Objects.requireNonNull(c);
if (c == this)
throw new IllegalArgumentException();
if (maxElements <= 0)
return 0;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int n = Math.min(maxElements, count);
for (int i = 0; i < n; i++) {
c.add(first.item); // In this order, in case add() throws.
unlinkFirst();
}
return n;
} finally {
lock.unlock();
}
}
// Stack methods
/**
* @throws IllegalStateException if this deque is full
* @throws NullPointerException {@inheritDoc}
*/
public void push(E e) {
addFirst(e);
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E pop() {
return removeFirst();
}
// Collection methods
/**
* Removes the first occurrence of the specified element from this deque.
* If the deque does not contain the element, it is unchanged.
* More formally, removes the first element {@code e} such that
* {@code o.equals(e)} (if such an element exists).
* Returns {@code true} if this deque contained the specified element
* (or equivalently, if this deque changed as a result of the call).
*
* <p>This method is equivalent to
* {@link #removeFirstOccurrence(Object) removeFirstOccurrence}.
*
* @param o element to be removed from this deque, if present
* @return {@code true} if this deque changed as a result of the call
*/
public boolean remove(Object o) {
return removeFirstOccurrence(o);
}
/**
* Returns the number of elements in this deque.
*
* @return the number of elements in this deque
*/
public int size() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return count;
} finally {
lock.unlock();
}
}
/**
* Returns {@code true} if this deque contains the specified element.
* More formally, returns {@code true} if and only if this deque contains
* at least one element {@code e} such that {@code o.equals(e)}.
*
* @param o object to be checked for containment in this deque
* @return {@code true} if this deque contains the specified element
*/
public boolean contains(Object o) {
if (o == null) return false;
final ReentrantLock lock = this.lock;
lock.lock();
try {
for (Node<E> p = first; p != null; p = p.next)
if (o.equals(p.item))
return true;
return false;
} finally {
lock.unlock();
}
}
/**
* Appends all of the elements in the specified collection to the end of
* this deque, in the order that they are returned by the specified
* collection's iterator. Attempts to {@code addAll} of a deque to
* itself result in {@code IllegalArgumentException}.
*
* @param c the elements to be inserted into this deque
* @return {@code true} if this deque changed as a result of the call
* @throws NullPointerException if the specified collection or any
* of its elements are null
* @throws IllegalArgumentException if the collection is this deque
* @throws IllegalStateException if this deque is full
* @see #add(Object)
*/
public boolean addAll(Collection<? extends E> c) {
if (c == this)
// As historically specified in AbstractQueue#addAll
throw new IllegalArgumentException();
// Copy c into a private chain of Nodes
Node<E> beg = null, end = null;
int n = 0;
for (E e : c) {
Objects.requireNonNull(e);
n++;
Node<E> newNode = new Node<E>(e);
if (beg == null)
beg = end = newNode;
else {
end.next = newNode;
newNode.prev = end;
end = newNode;
}
}
if (beg == null)
return false;
// Atomically append the chain at the end
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (count + n <= capacity) {
beg.prev = last;
if (first == null)
first = beg;
else
last.next = beg;
last = end;
count += n;
notEmpty.signalAll();
return true;
}
} finally {
lock.unlock();
}
// Fall back to historic non-atomic implementation, failing
// with IllegalStateException when the capacity is exceeded.
return super.addAll(c);
}
/**
* Returns an array containing all of the elements in this deque, in
* proper sequence (from first to last element).
*
* <p>The returned array will be "safe" in that no references to it are
* maintained by this deque. (In other words, this method must allocate
* a new array). The caller is thus free to modify the returned array.
*
* <p>This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this deque
*/
@SuppressWarnings("unchecked")
public Object[] toArray() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] a = new Object[count];
int k = 0;
for (Node<E> p = first; p != null; p = p.next)
a[k++] = p.item;
return a;
} finally {
lock.unlock();
}
}
/**
* Returns an array containing all of the elements in this deque, in
* proper sequence; the runtime type of the returned array is that of
* the specified array. If the deque fits in the specified array, it
* is returned therein. Otherwise, a new array is allocated with the
* runtime type of the specified array and the size of this deque.
*
* <p>If this deque fits in the specified array with room to spare
* (i.e., the array has more elements than this deque), the element in
* the array immediately following the end of the deque is set to
* {@code null}.
*
* <p>Like the {@link #toArray()} method, this method acts as bridge between
* array-based and collection-based APIs. Further, this method allows
* precise control over the runtime type of the output array, and may,
* under certain circumstances, be used to save allocation costs.
*
* <p>Suppose {@code x} is a deque known to contain only strings.
* The following code can be used to dump the deque into a newly
* allocated array of {@code String}:
*
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
*
* Note that {@code toArray(new Object[0])} is identical in function to
* {@code toArray()}.
*
* @param a the array into which the elements of the deque are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose
* @return an array containing all of the elements in this deque
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this deque
* @throws NullPointerException if the specified array is null
*/
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (a.length < count)
a = (T[])java.lang.reflect.Array.newInstance
(a.getClass().getComponentType(), count);
int k = 0;
for (Node<E> p = first; p != null; p = p.next)
a[k++] = (T)p.item;
if (a.length > k)
a[k] = null;
return a;
} finally {
lock.unlock();
}
}
public String toString() {
return Helpers.collectionToString(this);
}
/**
* Atomically removes all of the elements from this deque.
* The deque will be empty after this call returns.
*/
public void clear() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
for (Node<E> f = first; f != null; ) {
f.item = null;
Node<E> n = f.next;
f.prev = null;
f.next = null;
f = n;
}
first = last = null;
count = 0;
notFull.signalAll();
} finally {
lock.unlock();
}
}
/**
* Used for any element traversal that is not entirely under lock.
* Such traversals must handle both:
* - dequeued nodes (p.next == p)
* - (possibly multiple) interior removed nodes (p.item == null)
*/
Node<E> succ(Node<E> p) {
if (p == (p = p.next))
p = first;
return p;
}
/**
* Returns an iterator over the elements in this deque in proper sequence.
* The elements will be returned in order from first (head) to last (tail).
*
* <p>The returned iterator is
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* @return an iterator over the elements in this deque in proper sequence
*/
public Iterator<E> iterator() {
return new Itr();
}
/**
* Returns an iterator over the elements in this deque in reverse
* sequential order. The elements will be returned in order from
* last (tail) to first (head).
*
* <p>The returned iterator is
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* @return an iterator over the elements in this deque in reverse order
*/
public Iterator<E> descendingIterator() {
return new DescendingItr();
}
/**
* Base class for LinkedBlockingDeque iterators.
*/
private abstract class AbstractItr implements Iterator<E> {
/**
* The next node to return in next().
*/
Node<E> next;
/**
* nextItem holds on to item fields because once we claim that
* an element exists in hasNext(), we must return item read
* under lock even if it was in the process of being removed
* when hasNext() was called.
*/
E nextItem;
/**
* Node returned by most recent call to next. Needed by remove.
* Reset to null if this element is deleted by a call to remove.
*/
private Node<E> lastRet;
abstract Node<E> firstNode();
abstract Node<E> nextNode(Node<E> n);
private Node<E> succ(Node<E> p) {
if (p == (p = nextNode(p)))
p = firstNode();
return p;
}
AbstractItr() {
// set to initial position
final ReentrantLock lock = LinkedBlockingDeque.this.lock;
lock.lock();
try {
if ((next = firstNode()) != null)
nextItem = next.item;
} finally {
lock.unlock();
}
}
public boolean hasNext() {
return next != null;
}
public E next() {
Node<E> p;
if ((p = next) == null)
throw new NoSuchElementException();
lastRet = p;
E x = nextItem;
final ReentrantLock lock = LinkedBlockingDeque.this.lock;
lock.lock();
try {
E e = null;
for (p = nextNode(p); p != null && (e = p.item) == null; )
p = succ(p);
next = p;
nextItem = e;
} finally {
lock.unlock();
}
return x;
}
public void forEachRemaining(Consumer<? super E> action) {
// A variant of forEachFrom
Objects.requireNonNull(action);
Node<E> p;
if ((p = next) == null) return;
lastRet = p;
next = null;
final ReentrantLock lock = LinkedBlockingDeque.this.lock;
final int batchSize = 64;
Object[] es = null;
int n, len = 1;
do {
lock.lock();
try {
if (es == null) {
p = nextNode(p);
for (Node<E> q = p; q != null; q = succ(q))
if (q.item != null && ++len == batchSize)
break;
es = new Object[len];
es[0] = nextItem;
nextItem = null;
n = 1;
} else
n = 0;
for (; p != null && n < len; p = succ(p))
if ((es[n] = p.item) != null) {
lastRet = p;
n++;
}
} finally {
lock.unlock();
}
for (int i = 0; i < n; i++) {
@SuppressWarnings("unchecked") E e = (E) es[i];
action.accept(e);
}
} while (n > 0 && p != null);
}
public void remove() {
Node<E> n = lastRet;
if (n == null)
throw new IllegalStateException();
lastRet = null;
final ReentrantLock lock = LinkedBlockingDeque.this.lock;
lock.lock();
try {
if (n.item != null)
unlink(n);
} finally {
lock.unlock();
}
}
}
/** Forward iterator */
private class Itr extends AbstractItr {
Itr() {} // prevent access constructor creation
Node<E> firstNode() { return first; }
Node<E> nextNode(Node<E> n) { return n.next; }
}
/** Descending iterator */
private class DescendingItr extends AbstractItr {
DescendingItr() {} // prevent access constructor creation
Node<E> firstNode() { return last; }
Node<E> nextNode(Node<E> n) { return n.prev; }
}
/**
* A customized variant of Spliterators.IteratorSpliterator.
* Keep this class in sync with (very similar) LBQSpliterator.
*/
private final class LBDSpliterator implements Spliterator<E> {
static final int MAX_BATCH = 1 << 25; // max batch array size;
Node<E> current; // current node; null until initialized
int batch; // batch size for splits
boolean exhausted; // true when no more nodes
long est = size(); // size estimate
LBDSpliterator() {}
public long estimateSize() { return est; }
public Spliterator<E> trySplit() {
Node<E> h;
if (!exhausted &&
((h = current) != null || (h = first) != null)
&& h.next != null) {
int n = batch = Math.min(batch + 1, MAX_BATCH);
Object[] a = new Object[n];
final ReentrantLock lock = LinkedBlockingDeque.this.lock;
int i = 0;
Node<E> p = current;
lock.lock();
try {
if (p != null || (p = first) != null)
for (; p != null && i < n; p = succ(p))
if ((a[i] = p.item) != null)
i++;
} finally {
lock.unlock();
}
if ((current = p) == null) {
est = 0L;
exhausted = true;
}
else if ((est -= i) < 0L)
est = 0L;
if (i > 0)
return Spliterators.spliterator
(a, 0, i, (Spliterator.ORDERED |
Spliterator.NONNULL |
Spliterator.CONCURRENT));
}
return null;
}
public boolean tryAdvance(Consumer<? super E> action) {
Objects.requireNonNull(action);
if (!exhausted) {
E e = null;
final ReentrantLock lock = LinkedBlockingDeque.this.lock;
lock.lock();
try {
Node<E> p;
if ((p = current) != null || (p = first) != null)
do {
e = p.item;
p = succ(p);
} while (e == null && p != null);
if ((current = p) == null)
exhausted = true;
} finally {
lock.unlock();
}
if (e != null) {
action.accept(e);
return true;
}
}
return false;
}
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
if (!exhausted) {
exhausted = true;
Node<E> p = current;
current = null;
forEachFrom(action, p);
}
}
public int characteristics() {
return (Spliterator.ORDERED |
Spliterator.NONNULL |
Spliterator.CONCURRENT);
}
}
/**
* Returns a {@link Spliterator} over the elements in this deque.
*
* <p>The returned spliterator is
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}.
*
* @implNote
* The {@code Spliterator} implements {@code trySplit} to permit limited
* parallelism.
*
* @return a {@code Spliterator} over the elements in this deque
* @since 1.8
*/
public Spliterator<E> spliterator() {
return new LBDSpliterator();
}
/**
* @throws NullPointerException {@inheritDoc}
*/
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
forEachFrom(action, null);
}
/**
* Runs action on each element found during a traversal starting at p.
* If p is null, traversal starts at head.
*/
void forEachFrom(Consumer<? super E> action, Node<E> p) {
// Extract batches of elements while holding the lock; then
// run the action on the elements while not
final ReentrantLock lock = this.lock;
final int batchSize = 64; // max number of elements per batch
Object[] es = null; // container for batch of elements
int n, len = 0;
do {
lock.lock();
try {
if (es == null) {
if (p == null) p = first;
for (Node<E> q = p; q != null; q = succ(q))
if (q.item != null && ++len == batchSize)
break;
es = new Object[len];
}
for (n = 0; p != null && n < len; p = succ(p))
if ((es[n] = p.item) != null)
n++;
} finally {
lock.unlock();
}
for (int i = 0; i < n; i++) {
@SuppressWarnings("unchecked") E e = (E) es[i];
action.accept(e);
}
} while (n > 0 && p != null);
}
/**
* @throws NullPointerException {@inheritDoc}
*/
public boolean removeIf(Predicate<? super E> filter) {
Objects.requireNonNull(filter);
return bulkRemove(filter);
}
/**
* @throws NullPointerException {@inheritDoc}
*/
public boolean removeAll(Collection<?> c) {
Objects.requireNonNull(c);
return bulkRemove(e -> c.contains(e));
}
/**
* @throws NullPointerException {@inheritDoc}
*/
public boolean retainAll(Collection<?> c) {
Objects.requireNonNull(c);
return bulkRemove(e -> !c.contains(e));
}
/** Implementation of bulk remove methods. */
@SuppressWarnings("unchecked")
private boolean bulkRemove(Predicate<? super E> filter) {
boolean removed = false;
Node<E> p = null;
final ReentrantLock lock = this.lock;
Node<E>[] nodes = null;
int n, len = 0;
do {
// 1. Extract batch of up to 64 elements while holding the lock.
long deathRow = 0; // "bitset" of size 64
lock.lock();
try {
if (nodes == null) {
if (p == null) p = first;
for (Node<E> q = p; q != null; q = succ(q))
if (q.item != null && ++len == 64)
break;
nodes = (Node<E>[]) new Node<?>[len];
}
for (n = 0; p != null && n < len; p = succ(p))
nodes[n++] = p;
} finally {
lock.unlock();
}
// 2. Run the filter on the elements while lock is free.
for (int i = 0; i < n; i++) {
final E e;
if ((e = nodes[i].item) != null && filter.test(e))
deathRow |= 1L << i;
}
// 3. Remove any filtered elements while holding the lock.
if (deathRow != 0) {
lock.lock();
try {
for (int i = 0; i < n; i++) {
final Node<E> q;
if ((deathRow & (1L << i)) != 0L
&& (q = nodes[i]).item != null) {
unlink(q);
removed = true;
}
}
} finally {
lock.unlock();
}
}
} while (n > 0 && p != null);
return removed;
}
/**
* Saves this deque to a stream (that is, serializes it).
*
* @param s the stream
* @throws java.io.IOException if an I/O error occurs
* @serialData The capacity (int), followed by elements (each an
* {@code Object}) in the proper order, followed by a null
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
final ReentrantLock lock = this.lock;
lock.lock();
try {
// Write out capacity and any hidden stuff
s.defaultWriteObject();
// Write out all elements in the proper order.
for (Node<E> p = first; p != null; p = p.next)
s.writeObject(p.item);
// Use trailing null as sentinel
s.writeObject(null);
} finally {
lock.unlock();
}
}
/**
* Reconstitutes this deque from a stream (that is, deserializes it).
* @param s the stream
* @throws ClassNotFoundException if the class of a serialized object
* could not be found
* @throws java.io.IOException if an I/O error occurs
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
count = 0;
first = null;
last = null;
// Read in all elements and place in queue
for (;;) {
@SuppressWarnings("unchecked") E item = (E)s.readObject();
if (item == null)
break;
add(item);
}
}
void checkInvariants() {
// assert lock.isHeldByCurrentThread();
// Nodes may get self-linked or lose their item, but only
// after being unlinked and becoming unreachable from first.
for (Node<E> p = first; p != null; p = p.next) {
// assert p.next != p;
// assert p.item != null;
}
}
}